23 April 2014

Bio-isobutanol producer Gevo, Inc. has come to an agreement with
Lufthansa under which the carrier will evaluate Gevo’s renewable jet fuel with the goal of
approving the alcohol-to-jet fuel (ATJ) for commercial aviation use. (Earlier post.)
Lufthansa’s testing is being supported through work with the European
Commission.

ATJ, like the Fischer-Tropsch pathway, has the potential to use
lignocellulosic waste as feedstock, but promises to do so at less cost
than Fischer-Tropsch.

—Alexander Zschocke, Lufthansa Group Senior
Manager Aviation Biofuels

Alcohols, noted researchers from Southwest Research Institute (SwRI), US Air Force Research Laboratory (AFRL), and Rentech, Inc. in a 2013 paper in the ACS journal Energy & Fuels, can be converted into hydrocarbons using a range of processes and a range of products depending upon the feed alcohol and the process selected.

Butanol (both normal- and iso-) can also be dehydrated and oligomerized into kerosene boiling range products. However, this approach will produce fuels with a limited hydrocarbon distribution. C8 oligomers are near the flash point limit for jet fuel; C12 hydrocarbons are nicely in the middle of the boiling range; and C16 hydrocarbons are near the distillation end point for kerosene. Thus, a fuel derived from butanol feedstocks will have a different distillation profile compared to conventional jet fuel paraffins.

… These differences in ATJ blend components from SPK paraffins derived from the FT or HEFA processes cause concern with turbine engine manufacturers because the different carbon distributions of the fuel might impact engine performance. ASTM subcommittees are addressing these issues. How ATJ fuels are incorporated into ASTM D7566 will depend upon the outcome of the extensive testing program with these blend components.

—Wilson et al.

Gevo has developed and demonstrated the technology to convert isobutanol into both aliphatic and aromatic hydrocarbons using known chemistry and existing refinery infrastructure:

Isobutanol produced from starch or biomass is dehydrated over an acidic catalyst to produce isobutylene, which is then further reacted to product mixtures of longer chain aliphatic hydrocarbons.

A portion of this material is reacted separately to form high density aromatic compounds.

Hydrogen gas, a byproduct of the aromatization reaction, is used to remove unsaturated bonds in the aliphatic material.

The hydrocarbons then are blended in proportions that can meet all ASTM standards for fuels: isooctane is a dimer of dehydrated isobutanol and is a major component of the premium value alkylates, a key gasoline component; a trimer of the isobutylene (dehydrated isobutanol) is a jet fuel blend stock; a polymer of four and five isobutylenes can make a diesel blend stock.

By using isobutanol as a renewable raw material for producing jet fuel, the resulting jet fuel has the mixtures of molecules typical of petro-based jet fuel making it directly compatible with engines and infrastructure. Renewable jet embodies the potential of cleaner, greener, and as we scale up, cost competitive drop-in fuels.

We greatly appreciate
Lufthansa's and the European Commission's support of this effort.
Through initiatives like this, the commercial airlines are seeking to
prove out ATJ and move it towards commercialization.

—Patrick Gruber, Gevo CEO

Gevo’s patented ATJ fuel is designed to be fully compliant with aviation fuel specifications and provide equal performance, including fit-for-purpose properties.

In December 2013, the US Army flew the Sikorsky UH-60 Black Hawk helicopter on a 50:50 blend of Gevo’s ATJ-8 (Alcohol-to-Jet)—a renewable, drop-in alternative fuel for JP8 derived from isobutanol. (Earlier post.)